Harrison S.P., Morfopoulos C., Dani K.G.S., Prentice I.C., Arneth A., Atwell B.J., Barkley M.P., Leishman M.R., Loreto F., Medlyn B.E., Niinemets U., Possell M., Peñuelas J., Wright I.J. (2013) Volatile isoprenoid emissions from plastid to planet. New Phytologist. 197: 49-57.EnllaçDoi: 10.1111/nph.12021
Approximately 1-2% of net primary production by land plants is re-emitted to the atmosphere as isoprene and monoterpenes. These emissions play major roles in atmospheric chemistry and air pollution-climate interactions. Phenomenological models have been developed to predict their emission rates, but limited understanding of the function and regulation of these emissions has led to large uncertainties in model projections of air quality and greenhouse gas concentrations. We synthesize recent advances in diverse fields, from cell physiology to atmospheric remote sensing, and use this information to propose a simple conceptual model of volatile isoprenoid emission based on regulation of metabolism in the chloroplast. This may provide a robust foundation for scaling up emissions from the cellular to the global scale. © 2012 New Phytologist Trust.
Kefauver S.C., Penuelas J., Ustin S. (2013) Using topographic and remotely sensed variables to assess ozone injury to conifers in the Sierra Nevada (USA) and Catalonia (Spain). Remote Sensing of Environment. 139: 138-148.EnllaçDoi: 10.1016/j.rse.2013.07.037
The capacity to remotely identify impacts of ozone on conifers in California, USA and Catalonia, Spain was investigated using remote sensing and terrain-driven GIS analyses related to plant water relations and ozone uptake. The Ozone Injury Index (OII) field metric applied to Pinus ponderosa and Pinus jeffreyi in the USA and adapted to Pinus uncinata in Spain included visible chlorotic mottling, needle retention, needle length, and crown depth. Species classifications of AVIRIS and CASI hyperspectral imagery all approached 80% overall accuracy for the target bioindicator species. Remote sensing vegetation indices correlated best with longer-wavelength SWIR indices from the AVIRIS data in California, with the exception of the Photosynthetic Reflectance Index (PRI) correlation with the OII Visual Component (OIIVI), which was also the highest direct correlation in Catalonia. In Catalonia, the OIIVI alone and its subparts correlated better with the CASI data than with the full OII, namely the PRI (R2=0.28, p=0.0044 for OIIVI-amount and R2=0.33 and p=0.0016 for OIIVI-severity). Stepwise regression models of ozone injury developed using remote sensing indices combined with terrain-derived GIS variables were significant for OII in California (R2=0.59, p<0.0001) and in Catalonia (R2=0.68, p<0.0001 for OIIVI). Multiple regression models of ozone injury including a three year average of O3 exposure were significant both with imaging spectroscopy indices alone (R2=0.56, p<0.0001) and with topographic variables added (R2=0.77, p<0.0001) in Catalonia. Applying the multivariate models to image classifications could provide useful maps useful for ozone impact monitoring but requires further validation before being considered operational. © 2013 Elsevier Inc.
Llusia J., Penuelas J., Guenther A., Rapparini F. (2013) Seasonal variations in terpene emission factors of dominant species in four ecosystems in NE Spain. Atmospheric Environment. 70: 149-158.EnllaçDoi: 10.1016/j.atmosenv.2013.01.005
We studied the daily patterns in the rates of foliar terpene emissions by four typical species from the Mediterranean region in two days of early spring and two days of summer in 4 localities of increasing biomass cover in Northern Spain. The species studied were Thymelaea tinctoria (in Monegros), Quercus coccifera (in Garraf), Quercus ilex (in Prades) and Fagus sylvatica (in Montseny). Of the total 43 VOCs detected, 23 were monoterpenes, 5 sesquiterpenes and 15 were not terpenes. Sesquiterpenes were the main terpenes emitted from T. tinctoria. Total VOC emission rates were on average about 15 times higher in summer than in early spring. The maximum rates of emission were recorded around midday. Emissions nearly stopped in the dark. No significant differences were found for nocturnal total terpene emission rates between places and seasons. The seasonal variations in the rate of terpene emissions and in their chemical composition can be explained mainly by dramatic changes in emission factors (emission capacity) associated in some cases, such as for beech trees, with very different foliar ontogenical characteristics between spring and summer. The results show that temperature and light-standardised emission rates were on average about 15 times higher in summer than in early spring, which, corroborating other works, calls to attention when applying the same emission factor in modelling throughout the different seasons of the year. © 2013 Elsevier Ltd.
Morfopoulosl C., Prentice I.C., Keenan T.F., Friedlingstein P., Medlyn B.E., Penuelas J., Possell M. (2013) A unifying conceptual model for the environmental responses of isoprene emissions from plants. Annals of Botany. 112: 1223-1238.EnllaçDoi: 10.1093/aob/mct206
Background and Aims Isoprene is the most important volatile organic compound emitted by land plants in terms of abundance and environmental effects. Controls on isoprene emission rates include light, temperature, water supply and CO2 concentration. A need to quantify these controls has long been recognized. There are already models that give realistic results, but they are complex, highly empirical and require separate responses to different drivers. This study sets out to find a simpler, unifying principle. Methods A simple model is presented based on the idea of balancing demands for reducing power (derived from photosynthetic electron transport) in primary metabolism versus the secondary pathway that leads to the synthesis of isoprene. This model's ability to account for key features in a variety of experimental data sets is assessed. Key results The model simultaneously predicts the fundamental responses observed in short-term experiments, namely: (1) the decoupling between carbon assimilation and isoprene emission; (2) a continued increase in isoprene emission with photosynthetically active radiation (PAR) at high PAR, after carbon assimilation has saturated; (3) a maximum of isoprene emission at low internal CO2 concentration (ci) and an asymptotic decline thereafter with increasing ci; (4) maintenance of high isoprene emissions when carbon assimilation is restricted by drought; and (5) a temperature optimum higher than that of photosynthesis, but lower than that of isoprene synthase activity. ConclusionsAsimple modelwas used to test the hypothesis that reducing power available to the synthesis pathway for isoprene varies according to the extent to which the needs of carbon assimilation are satisfied. Despite its simplicity the model explains much in terms of the observed response of isoprene to external drivers aswell as the observed decoupling between carbon assimilation and isoprene emission. The concept has the potential to improve globalscale modelling of vegetation isoprene emission. © The Author 2013.
Mulder C., Ahrestani F.S., Bahn M., Bohan D.A., Bonkowski M., Griffiths B.S., Guicharnaud R.A., Kattge J., Krogh P.H., Lavorel S., Lewis O.T., Mancinelli G., Naeem S., Penuelas J., Poorter H., Reich P.B., Rossi L., Rusch G.M., Sardans J., Wright I.J. (2013) Connecting the Green and Brown Worlds. Allometric and Stoichiometric Predictability of Above- and Below-Ground Networks. Advances in Ecological Research. 49: 69-175.EnllaçDoi: 10.1016/B978-0-12-420002-9.00002-0
We examine the potential of trait-based parameters of taxa for linking above- and below-ground ecological networks (hereafter 'green' and 'brown' worlds) to understand and predict community dynamics. This synthesis considers carbon, nitrogen and phosphorus-related traits, the abundance of component species and their size distribution across trophic levels under different forms of management. We have analysed existing and novel databases on plants, microbes and invertebrates that combine physico-chemical and biological information from (agro)ecosystems spanning the globe. We found (1) evidence that traits from above- and below-ground systems may be integrated in the same model and (2) a much greater than expected stoichiometric plasticity of plants and microbes which has implications for the entire food-web mass-abundance scaling. Nitrogen and phosphorus are primary basal resources (hence, drivers) and more retranslocation of P than of N from leaves will lead to higher N:P in the litter and soil organic matter. Thus, under nutrient-rich conditions, higher foliar concentrations of N and P are reflected by lower N:P in the brown litter, suggesting less P retranslocated than N. This apparent stoichiometric dichotomy between green and brown could result in shifts in threshold elemental ratios critical for ecosystem functioning. It has important implications for a general food-web model, given that resource C:N:P ratios are generally assumed to reflect environmental C:N:P ratios. We also provide the first evidence for large-scale allometric changes according to the stoichiometry of agroecosystems. Finally, we discuss insights that can be gained from integrating carbon and nitrogen isotope data into trait-based approaches, and address the origin of changes in δ13C and δ15N fractionation values in relation to consumer-resource body-mass ratios. © 2013 Elsevier Ltd.
Mänd P., Hallik L., Peñuelas J., Kull O. (2013) Electron transport efficiency at opposite leaf sides: Effect of vertical distribution of leaf angle, structure, chlorophyll content and species in a forest canopy. Tree Physiology. 33: 202-210.EnllaçDoi: 10.1093/treephys/tps112
We investigated changes in chlorophyll a fluorescence from alternate leaf surfaces to assess the intraleaf light acclimation patterns in combination with natural variations in radiation, leaf angles, leaf mass per area (LMA), chlorophyll content (Chl) and leaf optical parameters. Measurements were conducted on bottom- and top-layer leaves of Tilia cordata Mill. (a shadetolerant sub-canopy species, sampled at heights of 11 and 16 m) and Populus tremula L. (a light-demanding upper canopy species, sampled at canopy heights of 19 and 26 m). The upper canopy species P. tremula had a six times higher PSII quantum yield (ΦII) and ratio of open reaction centres (qP), and a two times higher LMA than T. cordata. These species-specific differences were also present when the leaves of both species were in similar light conditions. Leaf adaxial/abaxial fluorescence ratio was significantly larger in the case of more horizontal leaves. Populus tremula (more vertical leaves), had smaller differences in fluorescence parameters between alternate leaf sides compared with T. cordata (more horizontal leaves). However, optical properties on alternate leaf sides showed a larger difference for P. tremula. Intraspecifically, the measured optical parameters were better correlated with LMA than with leaf Chl. Species-specific differences in leaf anatomy appear to enhance the photosynthetic potential of leaf biochemistry by decreasing the interception of excess light in P. tremula and increasing the light absorptance in T. cordata. Our results indicate that intraleaf light absorption gradient, described here as leaf adaxial/abaxial side ratio of chlorophyll a fluorescence, varies significantly with changes in leaf light environment in a multi-layer multi-species tree canopy. However, this variation cannot be described merely as a simple function of radiation, leaf angle, Chl or LMA, and species-specific differences in light acclimation strategies should also be considered. © The Author 2013. Published by Oxford University Press. All rights reserved.
Obersteiner M., Penuelas J., Ciais P., Van Der Velde M., Janssens I.A. (2013) The phosphorus trilemma. Nature Geoscience. 6: 897-898.EnllaçDoi: 10.1038/ngeo1990
[No abstract available]
Owen S.M., Penuelas J. (2013) Volatile isoprenoid emission potentials are correlated with essential isoprenoid concentrations in five plant species. Acta Physiologiae Plantarum. 35: 3109-3125.EnllaçDoi: 10.1007/s11738-013-1344-4
This study offers new insight and data in support of the "opportunist hypothesis", which suggests that there might be a relationship between carotenoid and volatile isoprenoid production. Five species of volatile isoprenoid-emitting plants (Eucalyptus globulus, Eucalyptus gunnii, Mucuna pruriens, Lycopersicon esculentum and Quercus ilex) were exposed to a range of imposed and natural stress conditions over a period of a few weeks in order to generate different levels of isoprenoid production potential. Volatile isoprenoid emission potentials and carotenoid concentrations were measured in all species, and dimethylallyl diphosphate (DMAPP) concentrations were measured in E. globulus, E. gunnii, M. pruriens and L. esculentum. Generally, instantaneously emitted isoprenoid emission potentials were positively correlated with carotenoid concentrations, and were negatively correlated with DMAPP concentrations. In contrast, emission potentials of monoterpenes stored in tissue pools were negatively correlated with carotenoid concentrations, and positively correlated with DMAPP concentrations. Our results support the possibility of a link (either direct, e.g. via substrate availability, or indirect, e.g. via complementary functionality) between emission potential of the volatile isoprenoid compounds studied here, and carotenoid synthesis at time scales of days to weeks. © 2013 Franciszek Górski Institute of Plant Physiology, Polish Academy of Sciences, Kraków.
Peng S., Piao S., Ciais P., Myneni R.B., Chen A., Chevallier F., Dolman A.J., Janssens I.A., Penuelas J., Zhang G., Vicca S., Wan S., Wang S., Zeng H. (2013) Asymmetric effects of daytime and night-time warming on Northern Hemisphere vegetation. Nature. 501: 88-92.EnllaçDoi: 10.1038/nature12434
Temperature data over the past five decades show faster warming of the global land surface during the night than during the day. This asymmetric warming is expected to affect carbon assimilation and consumption in plants, because photosynthesis in most plants occurs during daytime and is more sensitive to the maximum daily temperature, Tmax, whereas plant respiration occurs throughout the day and is therefore influenced by both T max and the minimum daily temperature, Tmin. Most studies of the response of terrestrial ecosystems to climate warming, however, ignore this asymmetric forcing effect on vegetation growth and carbon dioxide (CO 2) fluxes. Here we analyse the interannual covariations of the satellite-derived normalized difference vegetation index (NDVI, an indicator of vegetation greenness) with Tmax and Tmin over the Northern Hemisphere. After removing the correlation between Tmax and T min, we find that the partial correlation between Tmax and NDVI is positive in most wet and cool ecosystems over boreal regions, but negative in dry temperate regions. In contrast, the partial correlation between Tmin and NDVI is negative in boreal regions, and exhibits a more complex behaviour in dry temperate regions. We detect similar patterns in terrestrial net CO2 exchange maps obtained from a global atmospheric inversion model. Additional analysis of the long-term atmospheric CO2 concentration record of the station Point Barrow in Alaska suggests that the peak-to-peak amplitude of CO2 increased by 23 ± 11% for a +1°C anomaly in T max from May to September over lands north of 51N, but decreased by 28 ± 14% for a +1°C anomaly in Tmin. These lines of evidence suggest that asymmetric diurnal warming, a process that is currently not taken into account in many global carbon cycle models, leads to a divergent response of Northern Hemisphere vegetation growth and carbon sequestration to rising temperatures. © 2013 Macmillan Publishers Limited. All rights reserved.
Penuelas J., Guenther A., Rapparini F., Llusia J., Filella I., Seco R., Estiarte M., Mejia-Chang M., Ogaya R., Ibanez J., Sardans J., Castano L.M., Turnipseed A., Duhl T., Harley P., Vila J., Estavillo J.M., Menendez S., Facini O., Baraldi R., Geron C., Mak J., Patton E.G., Jiang X., Greenberg J. (2013) Intensive measurements of gas, water, and energy exchange between vegetation and troposphere during the MONTES campaign in a vegetation gradient from short semi-desertic shrublands to tall wet temperate forests in the NW Mediterranean Basin. Atmospheric Environment. 75: 348-364.EnllaçDoi: 10.1016/j.atmosenv.2013.04.032
MONTES ("Woodlands") was a multidisciplinary international field campaign aimed at measuring energy, water and especially gas exchange between vegetation and atmosphere in a gradient from short semi-desertic shrublands to tall wet temperate forests in NE Spain in the North Western Mediterranean Basin (WMB). The measurements were performed at a semidesertic area (Monegros), at a coastal Mediterranean shrubland area (Garraf), at a typical Mediterranean holm oak forest area (Prades) and at a wet temperate beech forest (Montseny) during spring (April 2010) under optimal plant physiological conditions in driest-warmest sites and during summer (July 2010) with drought and heat stresses in the driest-warmest sites and optimal conditions in the wettest-coolest site. The objective of this campaign was to study the differences in gas, water and energy exchange occurring at different vegetation coverages and biomasses. Particular attention was devoted to quantitatively understand the exchange of biogenic volatile organic compounds (BVOCs) because of their biological and environmental effects in the WMB. A wide range of instruments (GC-MS, PTR-MS, meteorological sensors, O3 monitors,. .) and vertical platforms such as masts, tethered balloons and aircraft were used to characterize the gas, water and energy exchange at increasing footprint areas by measuring vertical profiles. In this paper we provide an overview of the MONTES campaign: the objectives, the characterization of the biomass and gas, water and energy exchange in the 4 sites-areas using satellite data, the estimation of isoprene and monoterpene emissions using MEGAN model, the measurements performed and the first results. The isoprene and monoterpene emission rates estimated with MEGAN and emission factors measured at the foliar level for the dominant species ranged from about 0 to 0.2mgm-2h-1 in April. The warmer temperature in July resulted in higher model estimates from about 0 to ca. 1.6mgm-2h-1 for isoprene and ca. 4.5mgm-2h-1 for monoterpenes, depending on the site vegetation and footprint area considered. There were clear daily and seasonal patterns with higher emission rates and mixing ratios at midday and summer relative to early morning and early spring. There was a significant trend in CO2 fixation (from 1 to 10mgCm-2d-1), transpiration (from1-5kgCm-2d-1), and sensible and latent heat from the warmest-driest to the coolest-wettest site. The results showed the strong land-cover-specific influence on emissions of BVOCs, gas, energy and water exchange, and therefore demonstrate the potential for feed-back to atmospheric chemistry and climate. •We present a multidisciplinary biosphere-atmosphere field campaign.•We measured a gradient from semi-desertic shrublands to wet temperate forests.•A wide range of instruments and vertical platforms were used.•Land cover strongly influenced emissions of BVOCs and gas, energy and water exchange.•Vegetation has strong potential for feed-back to atmospheric chemistry and climate. © 2013 Elsevier Ltd.
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